Boosting Solar-Driven CO Conversion to Ethanol via Single-Atom Catalyst with Defected Low-Coordination Cu-N Motif.

Cu-based catalysts have been shown to selectively catalyze CO photoreduction to C solar fuels. However, they still suffer from poor activity and low selectivity. Herein, we report a high-performance carbon nitride supported Cu single-atom catalyst featuring defected low-coordination Cu-N motif (Cu-N-V). Lead many recently reported photocatalysts and its Cu-N and Cu-N counterparts, Cu-N-V exhibits superior photocatalytic activity for CO reduction to ethanol and delivers 69.8 μmol g h ethanol production rate, 97.8 % electron-based ethanol selectivity, and a yield of ~10 times higher than Cu-N and Cu-N. Revealed by the extensive experimental investigation combined with DFT calculations, the superior photoactivity of Cu-N-V stems from its defected Cu-N configuration, in which the Cu sites are electron enriched and enhance electron delocalization. Importantly, Cu in Cu-N-V exist in both Cu and Cu valence states, although predominantly as Cu. The Cu sites support the CO activation, while the co-existence of Cu/Cu sites are highly conducive for strong *CO adsorption and subsequent *CO-*CO dimerization enabling C-C coupling. Furthermore, the hollow microstructure of the catalyst also promotes light adsorption and charge separation efficiency. Collectively, these make Cu-N-V an effective and high-performance catalyst for the solar-driven CO conversion to ethanol. This study also elucidates the C-C coupling reaction path via *CO-*CO to *COCOH and rate-determining step, and reveals the valence state change of partial Cu species from Cu to Cu in Cu-N-V during CO photoreduction reaction.